Sterilization indicators (also referred to as biological indicators) provide a means for determining whether a sterilizing machine, such as those used to sterilize surgical instruments in hospitals, is functioning properly and killing microorganisms that are present in the sterilization chamber during a sterilization procedure.
Sterilization indicators are recognized in the art as providing an accurate and precise means for testing the effectiveness of a sterilization procedure. Conventional sterilization indicators gauge the effectiveness of a sterilization procedure by monitoring the survival of a test microorganism contained within the sterilization indicator that is many times more resistant to the sterilization process than most organisms that would ordinarily be present by natural contamination. The sterilization indicator is exposed to a sterilization cycle and then incubated under conditions that will promote the growth of any surviving test microorganisms. If the sterilization cycle fails, the sterilization indicator generates a detectable signal indicating that the biological specimen survived. The detectable signal is commonly an indication such as a color change or the emission of a luminescent or fluorescent signal.
One well-known type of sterilization indicator employs spores from bacteria or fungi, which are very resistant to sterilization, to test the effectiveness of a sterilization procedure. A typical sterilization indicator has an outer container (e.g., tube, sleeve, or ampoule) made of a compressible, plastic material and a sealed inner container (e.g., tube, sleeve, or ampoule) made of a breakable material such as glass. A bacteria impermeable, gas transmissive covering on the outer container allows sterilant to enter the outer container during a sterilization procedure. Live spores on a piece of carrier are located between the walls of the outer container and the inner container. The inner container contains a growth medium that stimulates the growth of live spores. During the sterilization procedure, sterilant enters the outer container through the cap and contacts the spores within the carrier. After the sterilization procedure, the inner container is crushed by compressing the outer container, releasing the growth medium and bringing it into contact with the spores within the carrier. The indicator is then incubated under conditions that stimulate spore growth. If the sterilization procedure is ineffective, surviving spores will grow out and cause a pH indicator in the growth medium to change color, indicating that the sterilization cycle failed to kill the test population of microorganisms and may have failed to kill contaminating microorganisms present in the sterilizer load. Although sterilization indicators that rely on the growth of spores are accurate, they are slow, commonly requiring between 1 and 7 days to provide final results.
In contrast to sterilization indicators that measure spore growth alone, enzyme indicators provide a rapid answer, often in a matter of a few hours. Such indicators measure the effectiveness of a sterilization procedure by measuring the activity of an enzyme whose activity is correlated with the destruction of contaminating microorganisms during a sterilization procedure. The indicators have a compressible outer container, a breakable inner container, and a cap that is bacteria impermeable but gas transmissive. Active enzyme is impregnated on a carrier located between the walls of the outer and inner containers, and a substrate that reacts with the active enzyme is contained within the sealed inner container. During the sterilization procedure the sterilant enters the outer container and contacts the active enzyme within the carrier. After the sterilization procedure, the inner vial is crushed and the enzyme strip is exposed to the substrate and incubated. If the sterilization procedure works properly, the enzyme is inactivated during the procedure and there is no detectable change following incubation. However, if the sterilization procedure is ineffective, the enzyme is not inactivated and will react with the substrate to form a detectable product. The enzyme-substrate product may be detectable as a color change or as a fluorescent or luminescent signal.
Dual rapid-readout indicators are sterilization indicators that test the effectiveness of a sterilization procedure by measuring both enzyme activity and spore growth following exposure to a sterilization procedure. The enzyme system gives a rapid indication of the effectiveness of a sterilization cycle, which is then confirmed by measurement of spore outgrowth over a longer period of time. In a dual rapid-readout indicator, the live spores utilized in the spore outgrowth portion of the indicator may also serve as the source of active enzyme for the enzyme activity portion of the assay. The rapid enzyme test measures the activity of an enzyme that is associated with the spores, and the spores themselves are then incubated to encourage the outgrowth of any spores that survived the sterilization procedure. 3M ATTEST 1291 and 1292 Rapid-readout Biological Indicators, available from 3M Company, St. Paul, Minn., are dual rapid-readout indicators that test the effectiveness of a sterilization cycle by measuring both the activity of an enzyme associated with Geobacillus stearothermophilus (formerly known as Bacillus stearothermophilis) spores in the indicator and the survival of the spores themselves.